Spiral conveyor apparatus with automatic flow control

ABSTRACT

A spiral conveyor with automatic flow control includes a plurality of curved segments connected to form a spiral for the flow by gravity of articles from an upper level to a lower level. Each of the segments includes freely rotating skate wheels forming a conveying surface and a controlled, powered cylindrical roller. A sensor mounted in each segment senses the presence of an article in the segment. A controller receives the signals from the sensors and activates the associated roller for transport mode to assist articles through the conveyor if the path is clear, or if the downstream portion of the conveyor is blocked, to reverse the roller for accumulate mode to hold articles in the segment until the path is cleared.

This application is a continuation of application Ser. No. 09/274,314,filed Mar. 23, 1999, which is a continuation application of applicationSer. No. 08/914,424, filed Aug. 19, 1997, now U.S. Pat. No. 5,901,827.

BACKGROUND AND SUMMARY

The invention is directed to roller conveyor systems using gravity tomove articles from an upper level to a lower level. More particularly,the present invention relates to a gravity powered spiral conveyorincluding means for assisting and controlling the movement of articlesthrough the conveyor.

A conveyor in accordance of the invention provides an apparatus forautomatically transporting articles from one level to a lower level orfor accumulating articles in the conveyor based on article movementconditions. The conveyor of the invention can be used as part of alarger conveyor system and is readily adaptable for providing a range ofheight changes and direction changes. While the invention is preferablydirected to a spiral conveyor, the inventive principles may be appliedto other conveyor configurations, as will be appreciated by thoseskilled in the art, and the invention is not necessarily limited to theembodiments described below.

A conveyor in accordance with the invention includes a frame preferablydefining a spiral conveying path from an upper level to a lower level. Aconveying surface is provided by a plurality of freely rotatable rollersor skate wheels. A plurality of controllable, reversible powered rollersare individually disposed in the frame at predetermined intervals alongthe conveying path. Sensing means is mounted in the frame to detect thepresence of conveyed articles adjacent each of the powered rollers. Thepowered rollers are controllable for assisting the gravity transport ofthe articles or for reversed rotation for accumulating articles in theconveyor when the downstream portion of the conveyor is full. Accumulatemode prevents articles from overloading the lower end of the conveyorwhen transport from the conveyor is blocked by holding the articles inthe conveyor. This facilitates resumption of transport when the blockedcondition is resolved.

According to the invention, a spiral conveyor includes a plurality ofcurved segments fastened to form a spiral path, each having apredetermined cant. The curvature and the cant of the segments can beselected so that the spiral executes a desired number of turns for aselected height change.

In accordance with a preferred embodiment of the invention, each of thesegments is shaped to define a 90° arc which simplifies manufacturingand assembly. The 90° segment arcs provide a convenient size for thetransport and accumulate modes of operation. In addition, 90° arcs allowthe entry segment and exit segment to be oriented at a convenientparallel or perpendicular direction to accommodate the directions of thefeed and takeaway conveyors.

According to another aspect of the invention, a powered roller isincluded in each of the segments to control the movement of a conveyedarticle through the segment. The powered rollers are controllable torotate alternatively in a forward direction to assist the transport ofarticles down the conveyor or a reverse direction to accumulate articlesin the conveyor.

According to yet another aspect of the invention, sensing means isincluded to sense the presence of an article in each of the segments. Asignal from the sensing means is used to control the powered rollers.Preferably, the sensing means comprises a plurality of sensors mountedin the conveyor with one sensor in each segment. The sensing means canbe any suitable device, for example, a photocell or a mechanical switch.

A control means receives the signals from the sensing means and uses thesignal to determine whether to activate the powered rollers fortransport mode or accumulate mode depending on a comparison of thepresence of articles in adjacent segments, that is, whether a downstreamsegment is clear to receive an article from the segment immediatelyupstream.

The control means operates in transport mode to activate a roller torotate in a forward direction in a segment when the sensing means sensesthe presence of the article in the segment and senses that thedownstream adjacent segment is clear.

In transport mode, the rollers rotate at a set speed in a direction forforward movement of the articles. Thus, articles of light weight thatmay have difficulty overcoming inertial or frictional forces on theconveyor are accelerated, and heavier articles that may move too fastfor the takeaway conveyor to handle smoothly are slowed down by frictionproduced in moving across the powered roller.

The control means operates in an accumulate mode upon sensing that anarticle has remained in a segment for a predetermined length of time.When accumulate mode is activated, the control means activates therollers in that segment to rotate in reverse to hold the article in thesegment, and as an article is sensed in the immediately upstreamsegment, that roller is rotated in reverse. The control means continuesto activate the segments in reverse sequence as long as a downstreamblockage exists. When the downstream segment clears, the control meansreverts to transport mode and activates the segments to resume movingarticles forward in the same order in which they were set in accumulatemode.

DESCRIPTION OF THE DRAWINGS

The invention will be better understood through the following detaileddescription in conjunction with the appended drawings, in which:

FIG. 1 is a schematic representation of a front view of a spiralconveyor in accordance with the invention;

FIG. 2 is a top view of the spiral conveyor of FIG. 1; and

FIG. 3 is a view of a conveyor segment in accordance with the invention

DETAILED DESCRIPTION

A conveyor system according to the invention is shown schematically inFIG. 1. The conveyor system 20 comprises a base 22 and a conveyor frame30 supported on the base. The conveyor frame 30 is formed as a spiraldescending from an upper entry level 32 to a lower exit level 34. Theconveyor frame 30 includes roller devices providing a conveying surfaceto allow an article 15 entering the conveyor frame 30 to travel by forceof gravity from the entry level 32 to the exit level 34. The spiralconveyor system 20 can be connected to a larger conveyor system having afeed conveyor 12 to deliver articles to the spiral conveyor 20 and atakeaway conveyor 14 to transport articles from the spiral conveyor to adownstream conveyor.

As seen in FIG. 2, the conveyor 30 according to the invention isassembled from a plurality of curved segments 40 a, 40 b, 40 c, and soon, mounted together on the base 22 to form the spiral conveyor frame30. According to a preferred embodiment, the segments are shaped to havea uniform, predetermined downward cant, which allows the segments to beconveniently joined to form a spiral spanning a desired height. Inaddition, the arcs preferably are formed as 90° arcs.

The cant can be selected so that the spiral provides a desired number offull or part turns for a given height change. The 90° turn of thesegments permits the entry and exit levels to be mutually oriented atany parallel or perpendicular direction. For example, if a feed conveyor12 having a direction A, as indicated by the arrow in FIG. 2, isconnected to segment 40 a, a takeaway conveyor can be connected, afteran appropriate number of intervening segments for a desired heightchange, at a desired exit direction parallel C or E, or perpendicular Bor D, to the feed conveyor 12 direction.

Conveyor segment arcs of 90° are convenient for manufacture andassembly, however, the segments 40 may be formed as other than 90° arcs,as is convenient for the particular installation, and the invention isnot limited to the embodiment described.

FIG. 3 illustrates in a highly simplified form a conveyor segment 40 inaccordance with the invention. The arrows indicate the direction oftravel for articles on the segment 40. The segment 40 includes a chassis42 supporting a plurality of roller devices 44. The roller devices 44can be skate wheels, as illustrated, or can be roller balls, cylindricalrollers, or other suitable devices.

Each segment 40 also includes a powered roller 50. The powered roller 50can be rotated alternatively in a direction to correspond with a forwardtravel direction of the segment, or in a reverse direction to resistforward movement. Powered, reversible rollers suitable for the apparatusaccording to the invention are available from several rollermanufacturers, for example, the Interroll Model 8.220P44D15 is one suchsuitable roller. The powered rollers 50 are provided with an outercoating of PVC to provide a suitable friction surface. The rollers 50rotate at a set speed and will add thrust to speed up slower moving,light weight articles and will drag on faster moving, heavier articlesto slow them, and will thus help make the flow of articles more uniform.

The powered roller 50 may be located at any convenient place on thesegment. For reasons of manufacturing convenience, the roller 50 ispreferably mounted at the exit end 46 of the segment. However, theroller can be positioned anywhere in the segment.

Each segment also includes a sensor 52 mounted on the chassis 42upstream of the powered roller 50. The sensor 52 detects the presence ofa conveyed article in the segment before it reaches the roller 50 andsends a signal to a controller 60, described below, for activating theroller. The sensor 52 is located a sufficient distance from the poweredroller 52 to allow the controller 60 to receive a signal from the sensorand to activate the roller to be rotating as the article reaches theroller. Preferably, the sensor 52 is positioned at about the midpoint oftravel of the segment. Alternatively, the sensor could be placed at anylocation upstream of the powered roller, and the controller 60 could beprogrammed to take into account the distance, if necessary.

According to a preferred embodiment of the invention, the sensor 52 is aphotoelectric device having a light source and a photocell, asillustrated. Other sensing devices may be used, for example, amechanical switch having a leaf interposed in the conveying path.

The controller 60 is a programmable microprocessor that is connected toreceive signals from each of the sensors 152 and, using thatinformation, to control the powered rollers 50 for either a transportmode or an accumulate mode.

According to a programmed operational method in accordance with theinvention, the controller 60 receives a signal from a sensor Nindicating that an article is present in segment N, where “N” indicatesany segment in the spiral conveyor. The controller 60 then checks thecondition of sensor N+1 in segment N+1 immediately downstream of segmentN (for the exit segment, the term “N+1” indicates a takeaway conveyorconnected at the exit segment). If sensor N+1 is clear, the controller60 activates roller N to rotate in a forward direction, whichcorresponds to transport mode. If sensor N+1 indicates an articlepresent, the controller checks for how long the sensor N+1 has indicatedthe presence of the article. If the duration of the “article present”signal from sensor N+1 is more than a predetermined time, the controlleractivates roller N to rotate in reverse to prevent the article insegment N from traveling to segment N+1. Subsequently, when the sensorN+1 indicates the segment is clear, the controller activates the rollerN to rotate in the forward transport direction and transport moderesumes.

When operating in transport mode, the controller coordinates therotation of the rollers to facilitate the movement of articles throughthe conveyor. As an article enters the spiral conveyor and is sensed bythe first sensor in the first segment, the controller determines whetherthe next downstream segment is clear. If so, the controller then startsthe first roller in forward, transport rotation. After the articlespasses the first roller, the first sensor senses that the article haspassed, and the controller turns the first roller off and starts thesecond roller in the second segment. As the article passes the secondroller and second sensor, the controller turns off the second roller andactivates the third roller in the third segment. This operationcontinues until the article passes the bottom segment. The system workscontinuously and will operate simultaneously for articles as they enterand travel through the various segments.

Accumulate mode will usually be initiated by a blocked condition at theexit conveyor segment 34. The controller will first activate the exitconveyor roller to rotate for accumulating articles, and will activatesegments sequentially, up to the entry conveyor if necessary. By way ofexample, the exit conveyor can become blocked because of a condition atthe takeaway conveyor 14 causing a backlog of articles. The controllerwill activate the exit roller to rotate in reverse to accumulatearticles if the sensor at the exit conveyor senses the presence of anarticle for predetermined time duration. The time duration issufficiently long to determine that an article has actually stopped atthe sensor (and is not merely slow moving), and a duration in the rangeof about 2 to 5 seconds has been found to be suitable. The time durationcan be adjusted for the size and normal transport speed of the articlesin the conveyor.

Depending on the size of the articles, the exit segment (and of course,each of the other segments) can accumulate at least one, and usuallyseveral articles. The accumulation of articles in the exit segment willeventually cause an article to stall in the preceding segment, thusblocking the preceding sensor. A signal from this preceding sensor tothe controller indicating the presence of an article for more than thepredetermined time will cause the controller to activate reverserotation of the associated roller, and accumulation will occur in thissegment. The change to accumulation mode continues upward through theconveyor as each segment senses the presence without movement of thearticles.

When the controller receives a signal that the takeaway conveyor isclear, the roller in the exit conveyor is changed to rotate fortransport, and the previously accumulated articles are transported tothe takeaway conveyor. The sensor in the exit conveyor will thenindicate that the exit conveyor is clear, and the controller will thenchange the next upstream roller to rotate in transport mode, thusreleasing articles from that segment, and so on up to the entry segment.

The controller can be programmed to determine whether the clear signalfrom a sensor has a predetermined duration, for example 2 seconds, toavoid changing to transport mode for simple shifts or slippage of thearticles in the exit conveyor.

It will be understood that Applicants' invention is not limited to theparticular embodiments that have been described and illustrated. Thisapplication contemplates any and all modifications that fall within thespirit and scope of Applicants' invention as defined by the followingclaims.

What is claimed is:
 1. A method for operating a gravity conveyor havingpowered rollers mounted at intervals to define a plurality of zones toassist and control transport of the articles, comprising the steps of:repeatedly monitoring each zone for the presence of an article in thezone; activating a powered roller in a zone for transport rotation whenan article is sensed in the zone and a next zone immediately downstreamis sensed as clear for transport; and controlling a powered roller in azone for accumulate mode when an article is sensed in the zone and anext zone immediately downstream is sensed as blocked.
 2. The method asclaimed in claim 1, wherein a zone is sensed as blocked if an article issensed in the zone for at least a predetermined time duration.
 3. Themethod as claimed in claim 1, wherein a zone is sensed as clear fortransport if no article is sensed in the zone for more than apredetermined time duration.
 4. The method as claimed in claim 1,further comprising the steps of sensing an article in an exit zone forat least a predetermined time duration and controlling an exit zonepowered roller in an accumulate mode.
 5. The method as claimed in claim4, further comprising the steps of sensing that a takeaway conveyor isclear for transport and changing the exit zone roller from accumulatemode to transport rotation.